The present invention relates to the expanding of various polymers to low density foams using novel blowing agents selected from the tertiary ethers, such as methyl tert-butyl ether, methyl tert-amyl ether, and ethyl tert-butyl ether.
The preparation of molded foamed plastic articles is well known wherein plastic particles are impregnated with organic blowing agents, expanded to preliminary low density particles, placed into a mold and finally heated to fill the mold and fuse the particles into the final article.
The most common polymer to be foamed commercially is polystyrene. For this polymer, the most common blowing agents are selected from the aliphatic hydrocarbons containing 4 to 6 carbon atoms in the molecule, including butane, pentane, cyclopentane, hexane, and cyclohexane. Unfortunately, these hydrocarbons are now considered to be hazardous to the atmosphere in the quantities which are released during the molding process.
Many other polymers would be useful in foam applications, but the hydrocarbon blowing agents are not soluble enough, or not retained for sufficient time in the other polymers to allow formation of desirable foams.
The Freon type blowing agents have greater solubility in polymers, less flammable, and were found to be suitable for many foam products, but have now been found to be detrimental to the ozone layers in the atmosphere.